1. Field of the Invention
The present invention relates to binoculars, and particularly to binoculars equipped with an image-blur correction mechanism.
2. Description of the Prior Art
A pair of binoculars is provided with two, right-hand and left-hand, optical systems, which are generally arranged such that their optical axes are symmetrical with each other. FIG. 13 shows the construction of a most typical type of binoculars in which each of the right and left optical systems consists of an objective lens 71, an eyepiece lens 72, and an image-erecting prism 73. Conventionally, alignment of the optical axes of binoculars is conducted at the last stage of the assembly process by a skilled worker, who, while observing an image through the binoculars, aligns manually the positions of optical components one by one or in groups until they are fixed in the best possible positions. In particular, the right and left objective lenses are arranged such that their optical axes are on the same plane and parallel to each other.
Recent years have seen the development of such binoculars that are equipped with an image-blur correction mechanism so that the observed image will not be blurred even if a shaking occurs, or such binoculars that are equipped with, in addition to an image-blur correction mechanism, an automatic focus adjustment function so that the focus position is adjusted automatically in accordance with the distance of the observed object as measured by the binoculars. Image-blur correction is usually achieved by providing correction lenses in the optical paths between the objective lenses and the eyepiece lenses, and driving those correction lenses to tilt the optical axes such that an image blur is canceled out. Even with binoculars incorporating such advanced features, alignment of the optical axes of the right and left optical systems is still conducted manually as ever.
With binoculars having permanently fixed optical axes, a remote object can be observed without any problem, because the image of the object is formed substantially at the center of the field of view of each of the right and left optical systems. However, as the object comes closer, its image moves away from the center, with the result that the image of a very close object is formed out of the field of view of each of the right and left optical systems. This problem is due to parallax, and can be solved by tilting the right and left optical axes in accordance with the object distance. Various methods for tilting the right and left optical axes are known; for example, European Patent Application No. EP 0 636 916 A1 discloses a technique of tilting optical axes by use of an image-blur correction mechanism.
Conventional optical-axis alignment, which is conducted manually throughout up to its final fine-alignment step, not only demands a great deal of time, but also tends to leave small alignment errors, making it difficult to realize the optical performance as designed.